Simple version of image similarity comparison implemented in PHP, _PHP tutorial

/**  
* 图像图像上度上下载  
*  
* @version $Id: ImageHash.php 4429 2012-04-17 13:20:31Z jax $
* @author jax.hu
*  
*    <br> *  //Sample_1   <br> *  $aHash = ImageHash::hashImageFile('wsz.11.jpg');   <br> *  $bHash = ImageHash::hashImageFile('wsz.12.jpg');   <br> *  var_dump(ImageHash::isHashSimilar($aHash, $bHash));   <br> *   <br> *  //Sample_2   <br> *  var_dump(ImageHash::isImageFileSimilar('wsz.11.jpg', 'wsz.12.jpg'));   <br> *   
*/   
   
class ImageHash {   
   
   /**Sampling rate 1~10
* @access public
* @staticvar int
**/   
   public static $rate = 2;   
   
   /**Similarity allowed value 0~64
* @access public
* @staticvar int
**/   
   public static $similarity = 80;   
   
   /**The opening function corresponding to the image type
* @access private
* @staticvar string
**/   
   private static $_createFunc = array(   
       IMAGETYPE_GIF   =>'imageCreateFromGIF',   
       IMAGETYPE_JPEG  =>'imageCreateFromJPEG',   
       IMAGETYPE_PNG   =>'imageCreateFromPNG',   
       IMAGETYPE_BMP   =>'imageCreateFromBMP',   
       IMAGETYPE_WBMP  =>'imageCreateFromWBMP',   
       IMAGETYPE_XBM   =>'imageCreateFromXBM',   
   );   
   
   
   /**Create image from file
* @param string $filePath file address path
* @return resource When the image is successfully opened, the image resource ID is passed, if it fails, it is false
**/   
   public static function createImage($filePath){   
       if(!file_exists($filePath)){ return false; }   
   
       /*判断文件类型是否可以开启*/   
       $type = exif_imagetype($filePath);   
       if(!array_key_exists($type,self::$_createFunc)){ return false; }   
   
       $func = self::$_createFunc[$type];   
       if(!function_exists($func)){ return false; }   
   
       return $func($filePath);   
   }   
   
   
   /**hash image
* @param resource $src image resource ID
* @return string image hash value, false if failed
**/   
   public static function hashImage($src){   
       if(!$src){ return false; }   
   
       /*缩小图片尺寸*/   
       $delta = 8 * self::$rate;   
       $img = imageCreateTrueColor($delta,$delta);   
       imageCopyResized($img,$src, 0,0,0,0, $delta,$delta,imagesX($src),imagesY($src));   
   
​ ​ ​ /*Calculate the grayscale value of the image*/  
            $grayArray = array();                                           for ($y=0; $y<$delta; $y++){
for ($x=0; $x<$delta; $x++){
                     $rgb = imagecolorat($img,$x,$y);                                                                          $col = imagecolorsforindex($img, $rgb);                                                                         $gray = intval(($col['red']+$col['green']+$col['blue'])/3)& 0xFF;  
$grayArray[] = $gray;
                                                                                                                                               Imagedestroy($img);
 
​ ​ ​ /*Calculate the grayscale average of all pixels*/  
          $average = array_sum($grayArray)/count($grayArray);                                                  
            /*Calculate hash value*/                                                                           $hashStr = '';                                               foreach ($grayArray as $gray){
               $hashStr .= ($gray>=$average) ? '1' : '0';                                                                         
         return $hashStr;                                       }  
 
 
/**hash image file
* @param string $filePath file address path
* @return string image hash value, false if failed
**/ 
Public static function hashImageFile($filePath){
            $src = self::createImage($filePath);                                                             $hashStr = self::hashImage($src);                                                     Imagedestroy($src);
 
         return $hashStr;                                       }  
 
 
/**Compare two hash values ​​to see if they are similar
* @param string $aHash The hash value of A picture
* @param string $bHash The hash value of the B picture
* @return bool Pass true when the pictures are similar, otherwise false
**/ 
Public static function isHashSimilar($aHash, $bHash){
$aL = strlen($aHash); $bL = strlen($bHash);
If ($aL !== $bL){ return false; }
 
​ ​ ​ /*Calculate the amount of allowable gap*/  
          $allowGap = $aL*(100-self::$similarity)/100;                                                
​ ​ ​ /*Calculate the Hamming distance of two hash values*/  
          $distance = 0;                                               for($i=0; $i<$aL; $i++){
If ($aHash{$i} !== $bHash{$i}){ $distance++; }
                                                                        
            return ($distance<=$allowGap) ? true : false;                                         }  
 
 
/**Compare two image files to see if they are similar
* @param string $aHash A picture path
* @param string $bHash B picture path
* @return bool Pass true when the pictures are similar, otherwise false
* */
Public static function isImageFileSimilar($aPath, $bPath){
        $aHash = ImageHash::hashImageFile($aPath);                                                           $bHash = ImageHash::hashImageFile($bPath);                                                             return ImageHash::isHashSimilar($aHash, $bHash);                                           }  
 
}